1932). Essential oils occur in some resins, but they are 
usually lost by oxidation in the fossilization process. 
In most studies of fossil remains, it has not been feasi- 
ble to carry out detailed structural analyses of the con- 
stituent acids, aleohols and resenes. It has been more 
practical to determine hardness, specific gravity, degree 
of solubility, kind of fluorescence, as well as elementary 
analyses such as carbon, hydrogen and oxygen ratios. 
The range of differences within these properties, how- 
ever, is neither sufficient to provide key characters for 
a classification system nor very helpful in the determina- 
tion of plant source. For example, although there is some 
variation, the empirical chemical composition of most 
ambers approaches C,,H,,O. The hardness varies from 1 
to 8 on Mohs scale or as soft as can be scratched by a 
fingernail to that scratched by a pocket knife. The de- 
gree of hardness may depend not only on chemical con- 
stitution, but also on the environmental conditions under 
which the resin dried or on the geological processes to 
which it has been subjected. Whether the resin remains 
tacky for a long period of time or dries readily may de- 
termine its degree of hardness. Furthermore, as Kirchner 
(1950) pointed out, hardness is greater in amber associated 
with wood than in that with aquatic inclusions. Submer- 
sion in water obviously provides conditions for solidifica- 
tion very different from those in the atmosphere, where 
each layer hardens as it emerges from tissues of the trunk. 
Resin contained in the roots solidifies under soil atmos- 
pheric conditions which may produce still another varia- 
tion in hardness. 
Specific gravity may vary from 1.00 to 1.25, but it 
commonly averages between 1.05 and 1.08 and hence 
is not a good distinguishing character. Melting points 
range from 150° C to 420° C; consequently, there is 
more variation evident here than in many other proper- 
[ 229 | 
